1. Field of the Invention
This invention relates to measuring light reflectance and, more particularly, to a scatterometer for measuring surface scatter of light from a sample being tested and a method of doing the same.
2. Prior Art
Surface scatter of light from optical components, such as mirrors, beamsplitters, etc., is an important means of measuring the geometry of surface microstructure and thus the quality of fabrication of these optical components and the quality of the materials used in their fabrication. Generally, there are three standard methods of measuring surface scatter or the roughness of a surface; profilometry (both mechanical and optical), global type measurements (i.e: collection of all scattered light over a hemisphere in terms of the ratio of scattered light to the incident light) and bidirectional reflectance distribution function (BRDF) measurements. BRDF measures angular scatter or the amount of power/sterradian as a function of angular departure from the surface normal vector. BRDF is also usually a function of the incidence angle.
In the past, BRDF has been used because it can produce more detailed information about the interaction of light with the surface being tested than profilometry or global type measurements. Generally, a detector would be provided which would swing about a sample 180.degree. and take sequential measurements of scattered power as a function of its angle in the plane of the incidence light beam. However, this process of moving a detector and taking sequential measurements is time consuming. In addition, the stability of the light source is critical in this sequential process to insure accurate measurements.
It is therefore an object of the present invention to provide for accurate bidirectional reflectance distribution function measurements in a fast manner.
It is a further object of the present invention to provide for parallel or simultaneous collection of data in a bidirectional reflectance distribution function measurement system.
It is a further object of the present invention to reduce the critical reliance on the stability of the light source in bidirectional reflectance distribution function measurement systems.